DESCRIPTION (provided by investigator): Obesity is a prevalent and serious medical condition. Behavioral treatment (BT) has become the standard of care for the (nonmedical) treatment of obesity, yielding both medically significant weight reductions and improvements in psychosocial functioning. However, long-term weight loss maintenance remains challenging. The obesogenic environment is one factor that appears to make weight loss maintenance difficult to achieve. Research suggests that a promising approach to improving the long-term results of BT is to place greater emphasis on modifying the structure, composition, and availability of food. Ongoing use of meal replacements (MRs) is one previously-supported way of doing so, but no randomized, controlled trial of this approach has tested its effectiveness during weight loss maintenance. Other promising nutritional methods for improving weight loss maintenance include decreasing food energy density and variety, increasing food structure and protein intake, and modifying individuals' personal food environments. We propose to combine these other nutritional methods into a treatment called Nutritrol. Integrating either MRs or the Nutritrol intervention into traditional BT could reduce or eliminate the weight regain that typically follows BT. The first aim of the proposed study is to determine if, relative to a standard BT condition, BT plus MR or BT plus Nutritrol will produce superior weight loss during treatment, better weight loss maintenance after treatment, or differential change in psychosocial outcomes. A second aim is to determine the degree to which the specific targets of the experimental interventions do in fact change in the anticipated direction during the intervention and to evaluate whether such changes might account for improvements in weight loss maintenance. This study is important because it could provide the first evidence that the current standard of care for obesity lifestyle treatment could be improved by the addition of MRs or a program of comprehensive nutritional change. The study design calls for randomly assigning overweight individuals to one of three treatment conditions: 1) BT, 2) BT+MR, or 3) BT+Nutritrol. Treatment will be carried out at Drexel University and the University of Pennsylvania. Each treatment will last 1 year and will be delivered through 75-minute sessions in a small group format. Treatment will be conducted on a weekly basis for months 1-6 and a bi-weekly basis for months 7-12. Following termination of treatment, participants will be followed for 1 year. Assessments will be completed at baseline, 6 months, 12 months (i.e., end of treatment), and at 6- and 12- month follow-ups. Major outcome variables will include body weight, nutritional intake, and psychosocial measures.